Script to add and remove F-Curve Modifiers to multiple selected f-cruves
import bpy
D = bpy.data
# We can access by action name
fcurves = D.actions['Goon_proxyAction'].fcurves
for f in fcurves :
    # TO add
    m = f.modifiers.new('CYCLES')
    #To remove
    f.modifiers.remove(m)
    # To remove all 'CYCLES' type modifiers
    for m in f.modifiers:
       if (m.type == 'CYCLES'): 
           f.modifiers.remove(m)